1. Field of the Invention
This invention relates to an improved catalyst for producing .alpha.,.beta.-unsaturated aliphatic carboxylic acids via catalytic vapor-phase oxidation of the corresponding .alpha.,.beta.-unsaturated aliphatic aldehydes.
2. Description of the Prior Art
It is known that .alpha.,.beta.-unsaturated aliphatic carboxylic acids such as acrylic acid and methacrylic acid are prepared by a vapor-phase catalytic oxidation of .alpha.,.beta.-unsaturated aliphatic aldehydes such as acrolein and methacrolein. Various catalysts to be used for the oxidation have been proposed.
For example, the catalysts for production of acrylic acid from acrolein are disclosed in, for example, Japanese Patent Publications Nos. 22,850/1965, 1,775/1966, 1,622/1967, 17,195/1967, 9,045/1968, 12,129/1969, 12,886/1969, 26,287/1969, 44/1972, 48,371/1972, 16,493/1973, and 19,296/1973, and Japanese Patent Laid-open Publications Nos. 2,011/1971, 8,360/1972, 18,823/1972, and 43,922/1974.
These proposed technics have improved or solved the problems to some extent. However, so far as the present inventors are aware, they are not always useful or satisfactory from the industrial viewpoint. These conventional catalysts have some defects in the various requirements for industrial catalysts such as a high reaction rate, a high yield, a long life time, satisfactory mechanical strength, reproducibility of production, and a simple condition of reaction.
Whether a catalyst satisfies these requirements or not depends mainly upon the inherent characteristics of the catalytic composition. In other words, the properties of a catalyst are more or less limited by the catalytic composition, although they may be varied according to the method of preparation, the method of activation, the use of carriers, and the like. Therefore, it is clear that selection of a proper catalytic composition itself is important so as to obtain the better results.
A catalyst consisting essentially of antimony, nickel, molybdenum and vanadium, which is similar to that of the present invention which is to be described in detail later, is disclosed in Japenese Patent Laid-open Publication No. 18,823/1972. A catalyst consisting essentially of antimony, nickel, molybdenum, vanadium and tungsten, which is also similar to that of the present invention, is disclosed in Japanese patent Laid-open Publication No. 43,922/1974. The latter catalyst is improved as to the yield of acrylic acid from acrolein, the life time of catalyst, reproducibility of production and the like, and is superior to the former catalyst. For example, the yield of acrylic acid with the former catalyst is 84.2% at 270.degree. C, whereas the yield with the latter catalyst is 86.8 % at 250.degree. C.